The present invention relates to a process for isolating and purifying vanillin from aqueous alkaline solutions containing vanillin and related phenolic contaminants such as orthovanillin, acetovanillone, para-hydroxybenzaldehyde, and syringaldehyde, and the like.
It is known that vanillin can be made by oxidizing a lignin or lignosulfonate material, such as results from the kraft and sulfite cooking processes for producing pulp. The oxidation is carried out at elevated temperatures and pressures in the presence of an oxygen-containing gas in an alkaline solution. The resulting alkaline aqueous solution contains in addition to the desired vanillin, the unwanted contaminants, such as orthovanillin, acetovanillone, para-hydroxybenzaldehyde and syringaldehyde, which must be removed from the vanillin if the vanillin is to be of high purity and quality.
Numerous processes have been proposed for purifying vanillin from alkaline solutions. These include Sandborn U.S. Pat. No. 2,104,701. This patent treats by countercurrent extraction the aqueous alkaline solution of vanillin with a suitable water-immiscible solvent, such as normal butyl alcohol, and recovers the solvent for reuse. The vanillin is removed from the solvent and is subjected to further purification by any known means, such as by distilling the solvent as its water-binary mixture to leave the vanillin compound in an alkaline aqueous solution for further refining.
Other patents employing butyl alcohol extractions include U.S. Pat. Nos. 2,399,607, 2,104,701 and 2,489,200. Other patents employ propyl alcohol or isopropyl alcohol as the extractant, such as U.S. Pat. No. 2,721,221.
Other patents disclosed purification of vanillin by employing distillation treatments such as U.S. Pat. Nos. 2,506,540 and 2,745,796.
While the foregoing treatments are useful in purifying vanillin, it is desired to provide improved processes which more efficiently and effectively isolate and separate vanillin from its chemically related contaminating impurities. Accordingly, it is an object of the present invention to provide an efficient and effective process for removing and purifying vanillin from aqueous alkaline solutions containing contaminants.
It is also an object of the present invention to provide highly efficient and economical procedures for purifying vanillin.